The present invention relates to a heat processing device for processing large-sized substrates, for example, LCD substrates and the like by heating.
In the manufacture of liquid crystal displays (LCDs), a circuit pattern is formed by a so-called photolithography technique wherein a photoresist liquid is applied to an LCD substrate of glass to form a resist film thereon, and the resist film is then exposed to light according to the circuit pattern, followed by a developing process.
More specifically, for example, an LCD substrate is cleaned in a cleaning device and then subjected to an adhesion process in an adhesion device, and after the substrate is cooled in a cooling device, a photoresist film is coated on a surface of the LCD substrate in a resist coating device. Subsequently, the photoresist film is heated for baking in a heat processing device, and the substrate is exposed to a predetermined pattern of light in an exposure device. The LCD substrate which has thus been exposed to light is then applied with a developer and developed in a developing device and the developer is washed off with a rinsing liquid, thereby completing a developing process.
The heat processing device used for heating the LCD substrate in the above-described developing process comprises, for example, a hot plate on which the LCD substrate is placed, a heater for heating the LCD substrate through the hot plate, a ventilation cover arranged so as to define a processing space in cooperation with the hot plate and having a vent hole in the center of a ceiling thereof, and a shutter for shutting off the processing space.
Meanwhile, there has recently been an increasing demand for enlargement of LCD substrates, and large-sized substrates of, for example, 840.times.650 mm, which are much larger than conventional substrates of 650.times.550 mm, are in demand. However, when such a large-sized LCD substrate is subjected to the heating process as described above, the processing temperature is liable to become uneven within the surface of the LCD substrate. For example, the larger the size of the LCD substrate, the greater the difference in temperature between the central and peripheral portions of the LCD substrate tends to become.
Accordingly, when larger-sized LCD substrates are to be processed, factors that affect the processing temperature within the heat processing device need to be controlled more strictly. Variation in the temperature distribution of the LCD substrate can be caused by a variety of factors, and conceivably one of the factors is radiation of heat from the hot plate. Specifically, the bottom surface and side faces of the hot plate are exposed to the atmosphere within the processing space, and thus heat is liable to radiate therefrom, causing a temperature difference between the central and peripheral portions of the hot plate. Such a temperature difference of the hot plate eventually causes a temperature difference between the central and peripheral portions of the LCD substrate, with the result that thermal evenness on the surface of the LCD substrate lowers.
Ventilation of the processing space during the heating process is also a factor of the temperature difference. In the aforementioned baking process in which the photoresist film formed on the LCD substrate is heated, solvent (e.g., thinner) in the photoresist film volatilizes due to heat, and to remove the vapor of the solvent from the processing space, air is let out through the vent hole in the ventilation cover. The flow of air produced due to the ventilation brings about a drop of the temperature of the outside of the hot plate or the LCD substrate, and such a drop of temperature, or disturbance, causes a temperature difference between the central and peripheral portions of the hot plate or the LCD substrate.
Hot plates conventionally used are formed by casting with a heater built therein. As a result of a recent trend for larger-sized LCD substrates, there is a demand for hot plates having higher response to heat and smaller thickness and weight. However, the thickness of cast-type hot plates can only be reduced to 40 mm or thereabouts due to restrictions imposed by the manufacturing process, and thus cast-type hot plates are associated with drawbacks such as poor response to heat, difficulty in reducing weight, and increased height of the device.